Selenium Monochloride

Selenium monochloride
Names
	IUPAC name Selenium monochloride
	Other names Dichlorodiselenide, Diselenium dichloride, Selenium chloride, 1,2-dichlorodiselane
Identifiers
CAS Number	10025-68-0 ;
3D model (JSmol)	Interactive image;
ChemSpider	59591 ;
EC Number	233-037-8;
PubChem CID	66206;
UNII	2A5292FC4P ;
	InChI InChI=1S/Cl2Se2/c1-3-4-2 Key: VIEXQFHKRAHTQS-UHFFFAOYSA-N ; InChI=1/Cl2Se2/c1-3-4-2 Key: VIEXQFHKRAHTQS-UHFFFAOYAC;
	SMILES Cl[Se][Se]Cl;
Properties
Chemical formula	Se2Cl2
Molar mass	228.83 g/mol
Appearance	Reddish-brown oily liquid
Density	2.7741 g/cm3
Melting point	−85 °C (−121 °F; 188 K)
Boiling point	127 °C (261 °F; 400 K) at 0.997 atm
Solubility in water	insoluble
Solubility in other solvents	Soluble in chloroform, carbon disulfide, and acetonitrile
Magnetic susceptibility (χ)	−94.8·10−6 cm3/mol
Hazards
GHS pictograms
GHS Signal word	Danger
GHS hazard statements	H301, H311, H314, H331, H373, H410
GHS precautionary statements	P260, P261, P264, P270, P271, P273, P280, P301+310, P301+330+331, P302+352, P303+361+353, P304+340, P305+351+338, P310, P311, P312, P314, P321, P322, P330, P361, P363, P391, P403+233, P405
	Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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	Infobox references

Selenium monochloride is an inorganic compound with the formula Se₂Cl₂. Although it is called selenium monochloride, a more descriptive name might be diselenium dichloride. It is a reddish-brown, oily liquid that hydrolyses slowly. It exists in chemical equilibrium with SeCl₂, SeCl₄, chlorine, and elemental selenium.^[1] Selenium monochloride is mainly used as a reagent for the synthesis of Se-containing compounds.

Structure and properties

Selenium monochloride has the connectivity Cl-Se-Se-Cl. With a nonplanar structure, it has C₂ molecular symmetry, similar to hydrogen peroxide and sulfur monochloride. The Se-Se bond length is 2.23 Å, and the Se-Cl bond lengths are 2.20 Å. The dihedral angle is 87°.^[2]

Preparation

Early routes to selenium monochloride involved chlorination of elemental selenium.^[3] An improved method involves the reaction of a mixture of selenium, selenium dioxide, and hydrochloric acid:^[4]

3 Se + SeO₂ + 4 HCl → 2 Se₂Cl₂ + 2 H₂O

A dense layer of selenium monochloride settles from the reaction mixture, which can be purified by dissolving it in fuming sulfuric acid and reprecipitating it with hydrochloric acid. A second method for the synthesis involves the reaction of selenium with oleum and hydrochloric acid:^[4]

2 Se + 2 SO₃ + 3 HCl → Se₂Cl₂ + H₂SO₃ + SO₂(OH)Cl

The crude selenium monochloride is removed via separatory funnel. Selenium monochloride cannot be distilled without decomposition, even at reduced pressure.^[4]

In acetonitrile solutions, it exists in equilibrium with SeCl₂ and SeCl₄.^[5] Selenium dichloride degrades to the monochloride after a few minutes at room temperature:^[6]

3 SeCl₂ → Se₂Cl₂ + SeCl₄

Reactions

Selenium monochloride is an electrophilic selenizing agent, and thus it reacts with simple alkenes to give bis(β-chloroalkyl)selenide and bis(chloroalkyl)selenium dichloride. It converts hydrazones of hindered ketones into the corresponding selenoketones, the structural analogs of ketones whereby the oxygen atom is replaced with a selenium atom.^[7] Finally, the compound has been used to introduce bridging selenium ligands between the metal atoms of some iron and chromium carbonyl complexes.^[7]

References

↑ Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 978-0-08-037941-8.
↑ Kniep, Rüdiger; Körte, Lutz; Mootz, Dietrich (1 January 1983). "Kristallstrukturen von Verbindungen A₂X₂ (A = S, Se; X = Cl, Br)". Zeitschrift für Naturforschung B 38 (1): 1–6. doi:10.1515/znb-1983-0102.
↑ Lenher, Victor; Kao, C. H. (1925). "The Preparation of Selenium Monochloride and Monobromide". Journal of the American Chemical Society 47 (3): 772–774. doi:10.1021/ja01680a025.
↑ ^4.0 ^4.1 ^4.2 Fehér, F. "Diselenium Dichloride". In Handbook of Preparative Inorganic Chemistry; Brauer, G., Ed.; Academic Press: New York, 1963; Vol. 1; p 422-433.
↑ Lamoureux, Marc; Milne, John (1990). "Selenium chloride and bromide equilibria in aprotic solvents; a ⁷⁷Se NMR study". Polyhedron 9 (4): 589–595. doi:10.1016/S0277-5387(00)86238-5.
↑ Maaninen, Arto; Chivers, Tristram; Parvez, Masood; Pietikäinen, Jarkko; Laitinen, Risto S. (1999). "Syntheses of THF Solutions of SeX₂(X = Cl, Br) and a New Route to Selenium Sulfides Se_nS_8−n(n = 1−5): X-ray Crystal Structures of SeCl₂(tht)₂ and SeCl₂·tmtu". Inorganic Chemistry 38 (18): 4093–4097. doi:10.1021/ic981430h.
↑ ^7.0 ^7.1 Back, Thomas G.; Moussa, Ziad (2003). "Encyclopedia of Reagents for Organic Synthesis". Encyclopedia of Reagents for Organic Synthesis. doi:10.1002/047084289X.rn00201. ISBN 0471936235.

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[1] Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 978-0-08-037941-8.

[2] Kniep, Rüdiger; Körte, Lutz; Mootz, Dietrich (1 January 1983). "Kristallstrukturen von Verbindungen A₂X₂ (A = S, Se; X = Cl, Br)". Zeitschrift für Naturforschung B 38 (1): 1–6. doi:10.1515/znb-1983-0102.

[3] Lenher, Victor; Kao, C. H. (1925). "The Preparation of Selenium Monochloride and Monobromide". Journal of the American Chemical Society 47 (3): 772–774. doi:10.1021/ja01680a025.

[Feher-4] 4.0 ^4.1 ^4.2 Fehér, F. "Diselenium Dichloride". In Handbook of Preparative Inorganic Chemistry; Brauer, G., Ed.; Academic Press: New York, 1963; Vol. 1; p 422-433.

[5] Lamoureux, Marc; Milne, John (1990). "Selenium chloride and bromide equilibria in aprotic solvents; a ⁷⁷Se NMR study". Polyhedron 9 (4): 589–595. doi:10.1016/S0277-5387(00)86238-5.

[6] Maaninen, Arto; Chivers, Tristram; Parvez, Masood; Pietikäinen, Jarkko; Laitinen, Risto S. (1999). "Syntheses of THF Solutions of SeX₂(X = Cl, Br) and a New Route to Selenium Sulfides Se_nS_8−n(n = 1−5): X-ray Crystal Structures of SeCl₂(tht)₂ and SeCl₂·tmtu". Inorganic Chemistry 38 (18): 4093–4097. doi:10.1021/ic981430h.

[Back-7] 7.0 ^7.1 Back, Thomas G.; Moussa, Ziad (2003). "Encyclopedia of Reagents for Organic Synthesis". Encyclopedia of Reagents for Organic Synthesis. doi:10.1002/047084289X.rn00201. ISBN 0471936235.

v t e Selenium compounds
Se(−II)	Ag₂Se Al₂Se₃ CaSe Se²⁻
Se(0,I)	Se₃S₅
Se(I)	Se₂S₆ Se₂Cl₂ C₃H₇NO₂Se
Se(II)	SeS₂
Se(IV)	SeCl₄ SeF₄ SeO₂ SeS₂ SeOBr₂ SeOCl₂
Se(VI)	SeF₆ SeO₃ SeO₂F₂